The present invention relates to an optical module manufactured by assembling together optical elements, such as optical fibers, waveguides, lenses, light emitting devices, and light detecting devices, and to a method for assembling such an optical module.
Japanese Laid-Open Patent Publication 7-5341 describes a prior art optical collimator array, or an optical module. The prior art optical collimator array has an optical fiber array, which includes a plurality of optical fibers, a micro-lens array, which includes a plurality of lenses, and a spacer. The micro-lens array is fixed to the spacer so that an end portion of the micro-lens array is exposed from a light passage window of the spacer. The spacer is then fixed to the optical fiber array so that the optical axis of each optical fiber is aligned with the optical axis of an associated one of the lenses.
The spacer includes a retaining portion, which receives the micro-lens array, a bonding surface joined with the optical fiber array, and a groove extending parallel to the bonding surface and defining the window. The retaining portion is formed so that when the spacer is fixed to the optical fiber array, the distance between the end surfaces of the micro-lenses in the micro-lens array and the end surfaces of the corresponding optical fibers is equal to the focal distance of the micro-lenses.
Nowadays, the alignment of the optical fiber array and the micro-lens array is simplified to facilitate the manufacturing of the optical collimator array. More specifically, the micro-lenses are retained in the spacer, and the spacer is bonded with an end portion of the optical fiber array. This optimizes the distance (Z axis position) between the micro-lenses and the optical fibers. The employment of such a spacer, which is machined with high accuracy, reduces the number of operations performed to adjust the alignment of the optical collimator array.
The optical fiber array includes two reference light fibers, which are used to position the micro-lenses. The two reference light fibers are each arranged at one of the two lateral ends of the optical fiber array. Beams of light emitted from the micro-lenses via the optical fibers and beams of light directly emitted from the two reference fibers are each received by a CCD camera and shown on a monitor. The beam of lights emitted from the two reference light fibers form two spots of light on the monitor. A reference line is defined by connecting the two spots of light. The spacer is fixed to the optical fiber array at a position where the beams of lights emitted from the micro-lenses fall on the reference line. This aligns the optical axis of each optical fiber with the optical axis of each micro-lens.
However, since the number of coordinates used for the alignment is decreased, the positioning of the micro-lens array and the optical fiber array may become improper. This may misalign the optical axes of the micro-lens array and the optical axes of the optical fiber array.
Further, the spacer, which has a complicated structure, must be machined with high accuracy to decrease the number of coordinates used for alignment. This increases the cost of the optical module.
When the optical fiber array is bonded with the optical fiber array at an aligned position, a V-shaped gap may be formed between the joining surface of the spacer and the end surface of the optical fiber end portion. Such V-shaped gap results in a bonding layer, which bonds the spacer and the optical fiber array, having an increased thickness. Such a thick bonding layer decreases reliability with regard to the fastening of the spacer to the micro-lens array and the optical fiber array.